The basic objective of this research proposal is to obtain data that will contribute to the understanding of peripheral vascular function. Problems will include: 1) microvascular volume changes by alterations in vessels dimension and indicator dilution techniques, 2) microvascular red cell and plasma distribution, 3) relationships between microvascular pressures and volumes, 4) reactivity of different sized pre- and post-capillary microvessels, 5) relationships between microvascular blood flow distribution and microvascular blood volume distribution, 6) relationships of changes in apparent capillary permeability to alterations in the above parameters and 7) effects of stimuli on capillary availability. Assessments will be made in several orders of magnitude of arterioles, capillaries, and venules and to relate these findings to changes on the whole organ level. Measurements of pressure, blood flow velocity (RBC velocity), microvessel dimension changes (length, diameter and volume) and transport of indicators through individual microvessels will be made. Comparison of changes in vessel volume as calculated from the mean transit time of indicators through the vessels will be made during vasomotor responses to various stimuli. Changes in capillary permeability with various experimental procedures will be assessed using fluorescein labelled dextrans of different molecular weights. The influence of the existing intraluminal blood pressure and vessel radius on the ability of the vessel to respond to standard stimuli will also be evaluated. The influences on resistance to blood flow is to be investigated. An understanding of the interrelationships between the various physiological parameters described in this proposal are basic to not only the normal situation but also of altered function and pathological conditions. They should serve as a means of quantitatively evaluating altered vasomotor function and reactivity during pathological processes such as hypertension, congestive failure of the circulation and shock.